Structure, fonctionnement, évolution des communautés benthiques ...

tel-00009359, version 1 - 1 Jun 2005
Chapitre 3 - Fonctionnement du réseau trophique benthique de la Grande Vasière
Figure 3: Distribution of stable-nitrogen isotope ratios (mean ± standard deviation) among The Great
Mud Bank food web. a Particulate Organic Matter (- 30 m), b Particulate Organic Matter (bottom),
1 Zooplankton, 2 Suprabenthos, 3 Ascidia sp., 4 C. subterranea, 5 H. fauveli, 6 A. opercularis, 7 N. sulcata,
8 A. glaber, 9 N. norvegicus, 10 M. rugosa, 11 T. stroemi, 12 L. impatiens, 13 C. allmani, 14 N. latericeus,
15 P. nouveli, 16 C. echinulatus, 17 Sepia sp., 18 N. caeca, 19 G. rhomboides, 20 L. depurator, 21 G. rouxii,
22 M. merluccius (8-15 cm), 23 L. typicus, 24 T. trachurus, 25 M. poutassou, 26 C. lyra, 27 S. desmaresti,
28 T. minutus, 29 M. merluccius (19-36 cm), 30 M. merluccius (39-47 cm).
Target species M. merluccius and N. norvegicus and their competitors
Each individual δ 13 C and δ 15 N value was plotted against size for the two main exploited
species, Merluccius merluccius and Nephrops norvegicus (Figures 4 (a and b) and 5 (a and b)), and
linear regression (equations given in Table 2 was used to explore relationships between size (total
length for fishes or cephalothorax length for crustaceans). This analysis indicated that stable carbon
and nitrogen isotope ratios for hake (n = 43) increased significantly with size (+3‰, r² = 0.74, p <
0.0001 for δ 15 N; +1.5‰, r² = 0.56, p < 0.0001 for δ 13 C).
δ 15 N
16
15
14
13
12
11
10
a b
0 10 20 30 40 50
Length (cm)
230
δ 13 C
-14
-15
-16
-17
-18
-19
0 10 20 30 40 50
Length (cm)
Figure 4 (a): Relation between δ 15 N muscle and size length of Atlantic hake M. merluccius (n = 43) (b):
Relation between δ 13 C muscle and size length of Atlantic hake M. merluccius (n = 43).